This invention relates to novel, heat-stable polyester compositions. More particularly, this invention relates to saturated polyesters stabilized against thermal and oxidative and hydrolytic degradation by use of a synergistic combination comprising a cyclic, organic carbonate and an antioxidant.
The term "saturated polyester" encompasses a wide variety of materials which are of significant industrial and economic importance. Well-known polyester materials include polyester fibers, polyester tire cord, plasticizers, alkyds and polyester adhesives. For the purpose of this invention it is intended to include those polyesters having linear chain-like structures derived by reacting compounds such as dicarboxylic acids or their acid functioning derivatives with dihydric alcohols or by heating omega-hydroxycarboxylic acids; and those polyesters having cross-linked, three dimensional structures derived by reacting di- or polycarboxylic acids with diols or polyols; said polyesters or copolyesters may contain alkyl or aryl or cycloalkyl or other groups which are not ethylenically unsaturated.
It is well-known to those skilled in the art that most polyesters are relatively stable materials as compared with other types of polymers, e.g. polyvinyl acetate, polystyrene, polyurethanes, etc. It is also well known, however, that when polyesters are exposed to high temperatures, high humidity and air, as they often must during processing and application from the molten state, they tend to degrade badly with detrimental loss of physical and chemical properties. This condition often results in inferior products at best, or worse, it renders these materials useless in the intended application thereby contributing to substantial economic losses to manufacturer and end-user alike.
The various degradation processes have been widely studied, and a number of stabilizers, e.g. acidity reducing agents, antioxidants, etc., have been suggested to minimize degradation; all of these stabilizers, however, have a limited stabilizing effect at best and are relatively expensive.